1. Technical Field of the Invention
This application is a continuation of U.S. patent application Ser. No. 11/538,943, filed on Oct. 5, 2006, which claims benefit under 35 U.S.C. §119(e) to the filing date of U.S. provisional patent application No. 60/777,274, filed on Feb. 27, 2006, both filed by Frederick E. Frantz.
This invention relates to the fields of synchronized sensor arrangements, and especially to those arrangements wherein the sensors are physically distant from each other and in which wired interconnection is contraindicated.
2. Background of the Invention
Traditional control and data acquisition systems use integrated components or remote devices that are connected with wired signals. Such systems are applied to a variety of distributed components where it is desired to measure time from a synchronized starting time, such as industrial controls, scientific equipment, food preparation, and sporting event judging systems. A cyclic event in a control and data acquisition application is initiated by a specified start condition that is used to define the beginning of the event. It is highly desirable that all devices in the system are synchronized with the occurrence of the start condition so that the control functions and data acquisition are also synchronized system wide.
For example, as shown in FIG. 4, a swimming meet (30) is conducted in a swimming pool (31) which is divided into a number of swimming lanes. Contestants (e.g. swimmers in this example) start the event in a synchronized manner, such as the firing of a starter pistol, ringing of a bell, or dropping of a flag. In many arrangements, there is a starting official (33) equipped with a starter device, which is wired (34) to a judges' console (38), attended by and operated by one or more judges (39).
When the event is synchronously started, a signal is sent from the starting device to the judges' console via the wire (34), which triggers the start of a timer within the console. In a swimming event, each lane is provided with an individual finish judge (35), who is equipped with a stopping device, such as a control (36) wired (37) to the judges' console (38). When each lane judge determines that the contestant assigned to his or her lane has completed the event, the lane judge activates the control, which sends a signal via the wire (37) to the console. Upon receipt of each stopping device control signal, the console records or marks the timer value for that lane or contestant.
Such a wired system provides start synchronization for all stopping sensors by using a single, centralized timer, from which stop times are read. However, such wired systems can be difficult to install, especially on a temporary basis. For this swimming event example, the wires may have to be draped or dressed considerable distances to circumnavigate a pool perimeter, diving platforms, spectator seating, etc. As water is a pervasive substance, wired systems intended for installation in wet conditions require expensive sealant and containment technologies to achieve a durable product. Further, safety may be comprised for swimmers, operators, judges, etc., who must move about the area in which the timer system is installed, as draped cables may pose a tripping hazard, and may interfere with water drainage paths.
In other applications, such as industrial controls or scientific equipment the corresponding installation, reliability, and safety issue may be present for wired systems. For example, installation of a distributed, wired sensor system may require draping or dressing of cables around or above dangerous equipment, reliability may be challenged by the existence of liquid or vaporous substances such as acids or solvents, and safety may be compromised by causing tripping or drainage issues.